Windows security patches

I know this might be a dumb question, but I was wondering if windows security patches are really necessary? Because usually after installing them i get problems(bluescreen of death, freezes) with my computer. Sometimes i notice that the file size they list on the site isn't the same size as the file i'm dling. Is that wierd of wut.... Well i usually don't dl those patches and my computer seems to be doing fine. So are those patches really need, and how come those files aren't right size when i'm dling them?

Personally I think the security patches are extremely important. I don't care much about the other patches either and I do leave driver updates alone as long as everything is working properly.
You could try installing them with only the bare necessity's running in the background to avoid some of the BSOD's.
Could you give some examples of the discrepencies in size you're experiencing? I must admit I never paid much attention to that.

Ok for example i've tried dling the Q314147: Security Update, the one at the top of the critical updates, it states its only 127kb, but when i dl it its comes out to 160kb. Some of the others are like that too, i've notice. I just curious, why they are different, is it even possible for files likes these be changed? Most of the time when i dl stuff i make sure its same size as the site states. So this one is about 33kb bigger that is stated.

The next one down, "Security Update, March 7, 2002," when i dl it its abou 835kb, when it states its suppose to be 127kb. Well there is always a chance the site could have a typo in it, stating the wrong thing. Who knows maybe this is a dumb question, which may be pointless.

Strange indeed. Could this be a difference in languages?
I downloaded the Dutch version and that is 164 kB in size, where the Finnish version is 163 kB
(this is for Q314147)
Have a good night, I'll see if I can come up with some answers.